1. Field of the Invention
The field of this invention relates to fibers and filled molding compositions from polyimides and copolyimides prepared from tetramethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride (TMCDA) or a mixture of TMCDA and another dianhydride and diamines. These novel fibers and filled molding compositions are useful in fiber applications and as engineering plastics.
2. Background of the Invention
The process for the manufacture of polyimide and copolyimide from TMCDA is disclosed in companion applications filed the same day and having attorney docket numbers as follows 14,595, 21,074 and 14,630. All of these applications are incorporated herein by reference and made part of this application. As stated in the companion applications, it has been known to make polyimides from pyromellitic dianhydride and aromatic diamines. This is disclosed in U.S. Pat. No. 3,179,634 (1965). British Patent specification No. 570,858 discloses various processes for making fiber forming polymers. The references listed below disclose the preparation of polyimides starting with cyclobutane-1,2,3,4-tetracarboxylic dianhydride. F. Nakanishi and M. Hasegawa, Polymers, 14, 440 (1973). JA7123917-S27, JA7137733-S44, JA137734-S44, JA7219710-T23 and JA7219908-T23. Another reference of interest is U.S. Pat. No. 3,843,143. In reviewing all these references it is clear that fibers and filled compositions from copolyimides and polyimides derived from TMCDA have not been contemplated in the prior art.
The general object of this invention is to provide fibers and oriented fibers and molding compositions reinforced with glass fibers, glass beads, minerals or a mixture thereof and graphite fibers wherein the polyimides and copolyimides are derived from TMCDA and diamines. We have now found that novel fibers and filled polyimdes and copolyimide compositions can be obtained by reacting TMCDA or a mixture of TMCDA and other dianhydrides with diamines. These compositions can be filled with about 10 to 60 weight percent glass fibers, glass beads, minerals, or a mixture thereof or graphite fibers. Advantageously, the molding compositions may contain from 30 to 50 weight percent of glass fibers, glass beads, minerals or the mixture thereof or graphite fibers. Our studies have shown that the cost of the molding products derived from TMCDA may be reduced by substituting for part of the polymer up to 60 weight percent thereof with glass fibers, glass beads, minerals or graphite fibers. These glass filled polyimides and copolyimides are much more economical than molding compositions prepared without the use of the glass fibers, glass beads, minerals or graphite fillers. Novel fibers can also be prepared from the polyimides and copolyimides derived from TMCDA and this is indicated by the excellent physical properties of these copolyimides and polyimides. The copolyimides and polyimides based on TMCDA and diamines are suitably extruded at a temperature of about 270.degree. to 350.degree. C. through a fiber die having a multiplicity of holes of about 0.036 inch diameter each. Fiber strands are suitably taken up at 1-500 feet per minute, preferably at about 200-300 feet per minute. The fibers are suitably drawn at a temperature of at least 70.degree. C. advantageously in the range of about 70.degree. C. to 270.degree. C., preferably in the temperature range of about 100.degree. C. to 150.degree. C. to give fibers having a tenacity of about 2.2 grams per denier and an initial modulus of about 28 grams per denier. The use of polyimides as engineering plastics has been limited only by the relatively high cost; thus, when the inherent cost can be brought down, the commercial application of polyimides can be greatly expanded.
Suitably, in our process for the manufacture of the novel copolyimides about equal molecular amounts of the TMCDA-aromatic or aliphatic dianhydride mixture are reacted with a primary diamine. The molar ratio of the TMCDA dianhydride mixture to the primary diamine may be in the range of 1.2:1 to 1:1.2, preferably in the range of 1 to 1. Advantageously, the reaction is carried out at a temperature of about 30.degree. to 210.degree. C. for a period of about 4 to 6 hours in a nitrogen containing organic polar solvent such as 1-methyl-2-pyrrolidinone (NMP), N,N dimethylacetamide or pyridine.
We have found that polyimides can be formed by reacting TMCDA with diamines. TMCDA reacts readily with the diamine to form a high molecular weight polyimide. In this process both aliphatic and aromatic diamines can be polymerized with TMCDA to form high molecular weight polyimides.
Our process for the manufacture of the polyimides comprises reacting about equal molar amounts of TMCDA with a primary diamine. The molar ratio of TMCDA to the primary diamine may be in the range of 1.2:1 to 1:1.2, preferably in the range of 1 to 1. In a suitable method, the reaction is conducted as a batch reaction at a temperature of about 30 to 300.degree. C. for a period of about 2 to 24 hours in a nitrogen containing organic polar solvent such as 1-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide or pyridine. The polycondensation can also be carried out as a continuous process. The polycondensation can suitably be carried out at a temperature of 30.degree. C. to 300.degree. C., preferably at a temperature of 100.degree. C. to 200.degree. C. The water by-product in these reactions may be distilled off at 100.degree. to 150.degree. C., removed by a stream of nitrogen or azeotroped with an organic solvent such as xylene. The polymerization reaction can also be carried out in the melt under an inert atmosphere or in vacuum.
The copolyimides have the following recurring structure, wherein R is a divalent aliphatic or aromatic hydrocarbon radical and R' is a tetravalent aliphatic or aromatic hydrocarbon radical. ##STR1##
The radical R may be divalent aliphatic hydrocarbons of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising -O-, methylene, ##STR2##
The preferred structures for R are the following: ##STR3##
The preferred structures for R' are one of the following: ##STR4## The radical R is derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylenediamine, tetramethylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 4,4'-diaminodicyclohexylmethane, xylylene diamine and bis (aminomethyl) cyclohexane; suitable aromatic diamines useful in the process include para and meta-phenylenediamine, 4,4'-oxydianiline, thiobis (aniline), sulfonylbis (aniline), diaminobenzophenone, methylenebis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis (2-methylaniline), thiobis (2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890 (1970) and U.S. Pat. No. 4,016,140 (1972) both incorporated herein by reference. The preferred diamines are 4,4'-oxydianiline, 1,12-dodecanediamine, and 1,6-hexanediamine.
The dianhydrides are characterized by the following formula: ##STR5## wherein R' is a tetravalent organic radical selected from the group consisting of aromatic, aliphatic, cycloaliphatic, heterocyclic, combination of aromatic and aliphatic, and substituted groups thereof. However, the preferred dianhydrides are those in which the R' groups have at least 6 carbon atoms characterized by benzenoid unsaturation, i.e. alternate double bonds in a ring structure, wherein the 4 carbonyl groups of the dianhydride are each attached to separate carbon atoms and wherein each pair of carbonyl groups is directly attached to adjacent carbon atoms in the R' group to provide a 5-membered ring as follows: ##STR6## The preferred dianhydrides, as recited above, yield upon reaction with the diamines polyimide structures having outstanding physical properties. Illustrations of dianhydrides suitable for use in the present invention include: pyromellitic dianhydride; 2,3,6,7-naphthalene tetracarboxylic dianhydride; 3,3',4,4'-diphenyl tetracarboxylic dianhydride; 1,2,5,6-naphthalene tetracarboxylic dianhydride; 1,2,3,4-cyclopentane tetracarboxylic dianhydride; 2,2',3,3'-diphenyl tetracarboxylic dianhydride; 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride; 3,4-dicarboxyphenyl sulfone dianhydride; 2,3,4,5-pyrrolidine tetracarboxylic dianhydride; 3,4,9,10-perylene tetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl) ether dianhydride; ethylene tetracarboxylic dianhydride; 3,3',4,4'-benzophenonetetracarboxylic dianhydride; bis(3,4-dicarboxyphenyl)sulfide dianhydride; bis(3,4-dicarboxyphenyl)methane dianhydride; 1,4,5,8-naphthalenetetracarboxylic dianhydride, tricyclo [4.2.2.0.sup.2,5 ] dec-7-ene-3,4,9,10-tetracarboxylic dianhydride, 3,6-etheno-hexahydropyromellitic dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 1,3-dimethylcyclobutane-1,2,3,4-tetracarboxylic dianhydride. The preferred dianhydride is tricyclo [4.2.2.0.sup.2,5 ] dec-7-ene-3,9,9,10-tetracarboxylic dianhydride.
The polyimides have the following recurring structure wherein R is a divalent aliphatic or aromatic hydrocarbon radical. ##STR7## The radical R may be divalent aliphatic hydrocarbons of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising -O-, methylene, ##STR8## The radical R is derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylenediamine, tetra-methylenediamine, hexamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 4,4'-diaminodicyclohexylethane, xylylene diamine and bis(aminomethyl) cyclohexane. Suitable aromatic diamines useful in Applicant's process include para- and meta-phenylenediamine, 4,4-oxydianiline, thiobis-(aniline), sulfonylbis(aniline), diaminobenzophenone, methylenebis(aniline), benzidine, 1,5-diaminonaphthalene, oxybis(2-methylaniline), thiobis-(2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. No. 3,494,890 (1970) and U.S. Patent 4,016,140 (1972) both incorporated herein by reference. The preferred diamines are 1,6-hexanediamine, 1,12 dodecanediamine and 4,4-oxybisanaline or 4,4'-oxydianiline.
In some cases the polyimide and copolyimide may be further polymerized under "solid state polymerization" conditions. The term solid state polymerization refers to chain extensions of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. The solid state polymerization can be carried out below the melting point of the polyimide and can be conducted in several ways. However all techniques require heating the ground or pelletized polyimide below the melting point of the polyimide, generally at a temperature of about 200.degree. to 300.degree. C. while either sparging with an inert gas such as nitrogen or operating under a vacuum. In cases where the polyimides have a low melt temperature, they can be polymerized in the melt under vacuum in thin sections or using thin film reactors known in the art.
Injection molding of the polyimides and copolyimides is accompanied by injecting the polyimides into a mold maintained at a temperature of about 50.degree. C. to 150.degree. C. In this process a 20 second to 1 minute cycle is used with a barrel temperature of about 200.degree. C. to 350.degree. C. These temperatures will vary depending on the Tg and Tm of the polymer being molded.
The polyimides and copolyimides have excellent mechanical and thermal properties and can readily be molded into useful articles or formed into fibers, films, laminates or coatings. The physical properties of the polyimide made with 1,12-dodecanediamine and the glass-reinforced polyimide are shown on Table 2. Infrared spectra of the polyimides has confirmed the polyimide structure.
Analysis of the TMCDA-diamine polyimide by thermal gravimetric analysis shows excellent stability. This is demonstrated by the fact that under nitrogen atmosphere 1% weight loss occurs at a temperature of 310.degree. Centigrade and the main weight loss occurs at a temperature of about 400.degree. Centrigrade. Glass transition temperature Tg of the polyimide varied with the particular diamine used as shown in the Examples.
Diamines with the amino groups attached directly to the aromatic ring are suitably polymerized with TMCDA by solution condensation in organic polar solvents. Useful polar solvents include N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, N,N-dimethylformamide, pyridine, dimethylsulfoxide and the like.
We have found that the polyimides of this invention are improved by the addition of reinforcing material; particularly the mechanical properties of the polyimides are improved if these polyimides contain from about 25 to 60 percent by weight glass fibers, glass beads, minerals or graphite or mixtures thereof. In the preferred range the polyimides contain 30 to 40 percent by weight of the glass fibers, glass beads, or graphite or mixtures thereof. Suitably reinforcing materials can be glass fibers, glass beads, glass spheres, or glass fabrics. The glass fibers are made of alkali-free boron-silicate glass or alkali containing C-glass. The thickness of the fiber is suitably on the average between 3 mm and 30 mm. It is possible to use both long fibers with average lengths of from 5 to 50 mm and also short fibers of an average filament length from 0.05 to 5 mm. In principle, any standard commercial-grade fibers, especially glass fibers, may be used. Glass beads ranging from 5 mm to 50 mm in diameter may also be used as a reinforcing material.
The reinforced polyimide polymers may be prepared in various ways. For example, so-called rovings endless glass fiber strands are coated with the polyamic acid melt and subsequently granulated. The cut fibers or the glass beads may also be mixed with granulated polyamic acid and the resulting mixture melted in a conventional extruder, or alternatively the fibers may be directed, introduced into the polyamic acid melt through a suitable inlet in the extruder. Injection molding of the novel glass-filled polyimides and copolyimides is accomplished by injecting the polyimides into a mold maintained at a temperature of about 50.degree. to 150.degree. C. In this process a 20 second cycle is used with a barrel temperature of about 200.degree. to 350.degree. C. The injection molding conditions are given in Table 1.
TABLE I ______________________________________ Mold Temperature 50 to 150.degree. C. Injection Pressure 15,000 to 19,000 psi and held for 1 to 3 seconds Back Pressure 100 to 220 psi Cycle Time 20 seconds Extruder: Nozzle Temperature 200 to 350.degree. C. Barrels: Front heated to 200 to 350.degree. C. Screw: 20 to 25 revo- lutions/minute ______________________________________
The mechanical properties of the polyimide and copolyimide of the glass reinforced polyimides are given in Table 2, and show that these polyimides have excellent mechanical and thermal properties.
The following examples illustrate the preferred embodiment of the invention. It will be understood that the examples are for illustrative purposes only and do not purport to be wholly definitive with respect to conditions or scope of the invention.